Airworthiness Directives

The following directives were issued to the Airlines and Concordes manufactures by the CAA and DGAC on September 5th 2001:

The fitment of Kevlar lining to key fuel tanks ­ this will reduce the flow of fuel from any leak which may occur, which together with the removal of electrical ignition sources will make sustained fire impossible.

The use of the new Michelin Near Zero Growth (NZG) tyres on all eight main wheels - these tyres are designed to be more resilient to damage by foreign objects and only in extreme cases can smaller, lighter tread pieces be released, giving a much lower level of energy on impact than that which occurred at Gonesse.

The armouring of electrical wiring in the undercarriage bay - the investigators believe that the fire may have been ignited by an electrical spark in the undercarriage bay, and that protecting this area eliminates that risk.

The water deflector retention cable must (if fitted) be removed and there is a slight reprofiling of the deflector to accommodate the new tyre.

The antiskid protocols are changed. This is necessary because of the tyre change. (The anti-skid system is common to most airliners. If an aircraft is about to skid it automatically releases the brakes, for a short time, to prevent a skid developing.)

The flat tyre detection and warning system must be working on departure.

The electrical power to the brake cooling fans is switched off before take off and landing.

MODIFICATIONS TO CONCORDE

It was decided that the main cause of the accident was the ignition of the kerosene flowing from a massive rupture in a fuel tank caused by debris hitting the underside of the tank. After researching the possibilities for shielding the tanks the best source of protection was found to be lining the insides of certain tanks with kevlar-rubber panels.

These such panels (although not containing kevlar) were used on wartime Fighter aircraft protected their fuel tanks with a layer of rubber mounted on the inside of all the surfaces of the tanks, thus when bullets pierced the tanks, the rubber allowed the bullets through but then sealed the holes behind them, therefore preventing fuel from pouring out.

After the completion of the tests by an Air France Concorde (F-BVFB) at the Flight test centre (CEV) of Istres it was decided that these panels be fitted to Tanks 5 and 8 and to parts of tanks1,4,6 and 7 which would be susceptible to tyre debris damage from the Landing gear. These are shown in red on the diagram below. The liners are designed to reduced the flow rate due to any tank rupture to around 0.5 litres/sec. The rupture that caused the Paris accident was allowing fule to escape at around 100L/sec

Over 100 custom built liners are fitted into each aircraft a short distance above the tank base between the wing ribs. The liners for each aircraft have also had to be different as each individual Concorde was effectively hand built. Initially it was thought that a standard kit could be designed for each aircraft that could be modified, but the liners proved so strong that they had to be sent back to the manufacturer when alterations were required.

These panels are fitted individually into the tanks and then sealed together to give a fuel tight seal. The Kevlar-rubber panels have been designed to match the density of the fuel (O.792). The installation of these panels would displace some fuel, thus reducing very slightly the overall range of the aircraft, but should not significantly alter the centre of gravity and balance calculations.

The centre of gravity of Concorde is of uppermost importance as it is the main method of trimming the aircraft for minimum drag during supersonic flight. Another important factor that had to be considered was that the fuel is used to cool the airframe and so must still be able to circulate fully on top of and also under the liners.

The liners have small holes in them that allow the fuel to circulate both above and below the liners. The hole size is a compromise to allow the fuel to circulate correctly but also not cause any significant flow should a tank be ruptured. Test were carried out on a BA owned Rolls-Royce Olympus engine to confirm that the maximum expected flow rate of 0.5L/sec would not have any significant or adverse effect on the engine while running.

These modifications were prototyped on British Airways Concorde G-BOAF. Flight tests took place on this aircraft to prove effectiveness of the modifications and more importantly that they would have no adverse effect on the aircraft and its systems.

On the very first verification first flight, the potential problems the liners could have caused with fuel cooling, heat distribution in the fuel, fuel flow between tanks, fuel flow into the engines and the aircraft's centre of gravity, were not seen. On subsequent tests the results were confirmed paving the way for other aircraft in both the BA and Air France fleets to go though the multi-million pound modification programme.

There are other modifications which were also fitted: These include the fitting of the New Michelin NZG tyres (See below) along with armour plating for the cabling and hydraulics running through the main gear bays.

The normal operating procedures will be changed so that the 115V supply to the carbon brake cooling fans is deactivated during the takeoff run. It is felt that a short in this supply could have ignited the leaking fuel. These fans can then be turned back on once the undercarriage has been retraced to fully cool the brakes.

BA's Cabin Interior Upgrade

British Airways will also refit their cabin interiors at a cost of £2 Million UK per aircraft. These changes, which were planned before the fleet was grounded, include New seats, New washrooms, Interior design and tableware.

Interior experts Conran & Partners led by Sir Terence Conran advised on colours, fabrics and accessories working with London based consultancy Factory Design, the British Airways' Design and Brand Management teams and Britax Aircraft Interior Systems of Camberley, Surrey.
The Key features of the interior upgrade include:

New seats: In ink-blue Connolly leather and fabric with a cradle mechanism,
footrest and contoured headrest for more comfort and support, the new seats are
designed by London based agency Factory Design working with Britax-Contour
Aircraft Interior Systems. The design is inspired by the classic Charles & Ray
Eames chairs, and uses new technology and materials that are 20 per cent lighter.
The seats are constructed in carbon fibre, titanium, aluminium and covered in Connolly leather

New interiors: Much lighter and brighter with different lighting filters to give a
fresher look which changes to a cool blue 'wave' throughout the cabin when
Concorde flies through the sound barrier at Mach One (675mph).

New washrooms: New more spacious washrooms in aqua green and stainless
steel with opaque wall panels that are uplit and downlit, to give a sense of more
space. Linen towels and toiletries from Kiehls complement the style.

New Galleys: New lighter and more efficent gallerys will be fitted to the aircraft. The gallleys, both at the front and rear of the aircraft, will feature a 'Stanless Steel look' similar to that found in restaurant kitchens

New Machmeter: Improved Machmeters will be installed to replaced the marrilite displays that have been a feature of the aircraft for many years. The stylish new display will fit in with the ultra modern feel that the new overall look will provide, but also still give the information that the passgengers want to have their picture taken next to.

These new interiors will take advantage in using modern technologies which will result in a weight saving of 400Kg. This saving largely off-sets the additional weight being added to the fuel tanks by the Kevlar-rubber liners and means that Concorde can continue to operate at the range and capacity it enjoys at present, although the main saving is through the use of the new tyres which are 20Kgs lighter each.

Air France are understood to be considering a cabin upgrade to replace the interiors that were installed many years ago to upgrade the seating that was originally fitted to the aircraft when they were delivered in the 1970's

MICHELIN NZG TYRES

At EADS' request, Michelin was developed a
new tire technology for Concorde and other new aircraft such as the Airbus A340-600 and A380 'Super-Jumbo', the tyre had been in development at the time of last years crash(since 1999), but work was subsequently speeded up.

In the weeks that followed the tragic Concorde accident, EADS contacted
tyre manufacturers across the world, including Michelin, to find out if any
research was under way to improve the resistance of tires to damage by foreign
objects. Michelin unveiled its last innovation of radial technology: the
radial NZG.

This new aircraft tire technology, christened NZG for "Near Zero Growth",
uses a high-modulus reinforcement material. This offers higher damage
resistance and substantial weight gains, two key qualities in the field of
aviation.

" We think that this new tire will be a significant element for the process of re-certification of Concorde ", declared Pierre Desmarets, general manager of aviation activity at Michelin.

These tires were tested on an Air France Concorde (F-BTSD), again at Istres the military test base in the Rhone delta region of France, during a series of ground and flight tests that took place in May 2001.

MICHELIN NZG TYRE SPECS

External Diameter

110cm

Width

40cm

Weight

80kg

Tread

4 Groves

Pressure

16 Bar

Max Speed

280MPH

No. per Aircraft

8

Some of the text in this article was supplied by a UK based private pilot who published an article on the Internet during September 2000 at www.acestudio.co.uk/concorde.htm
This article outlined the use of a rubber based liner
used as the basis of the protection to fighter aircraft fuel tanks in the war.